1. Field of the Invention
The present invention relates in general to an automotive transmission, and more particularly to a toroidal type continuously variable transmission which generally comprises a forward/backward switching device with a planetary gear unit, a loading cam device and a toroidal type speed change unit which are coaxially arranged.
2. Description of the Prior Art
One of continuously variable transmissions of the toroidal type is shown in Laid-open Japanese Patent Application 5-039834. In the transmission, a torque from the forward/backward switching device is transmitted to the toroidal type speed change unit through the loading cam device. The planetary gear unit of the switching device is rotatably supported by a fixed annular wall member through a bearing. In order to suppress excessive rotation speed of the bearing at the time when the planetary gear unit rotates relative to the wall member, the bearing is positioned near a rotation center of the planetary gear unit where the bearing exhibits a smaller peripheral speed. For achieving this positioning, the fixed annular wall member extends radially inward to such a position as to face a pinion carrier of the planetary gear unit.
The toroidal type speed change unit comprises input and output cone discs and power (or friction) rollers each being put between the input and output discs to establish a frictional engagement therewith. By continuously changing the inclination angle of the power rollers relative to the input and output discs, speed change is continuously carried out during power transmission from the input disc to the output disc. To effectively make the power transmission from the input disc to the output disc, it is necessary to provide a condition wherein the power rollers are biased against the input and output discs in accordance with a transmitted torque. For this purpose, the loading cam device is employed.
The loading cam device comprises a cam disc which is arranged coaxial with the input disc and, cam rollers which are rotatably disposed between respective inclined cam surfaces of the cam disc and the input disc. The cam rollers are held by a holder in a manner to be regulated in relative positioning. The torque applied to the cam disc is transmitted to the cam rollers and then to the input disc. During this, the cam rollers are forced to roll on the respective inclined cam surfaces of the cam disc and the input disc to produce between the cam disc and the input disc a certain thrust in accordance with the transmitted torque. With the thrust thus produced, the power rollers are compressed between the input and output discs.
In the transmission of the publication, the forward/backward switching device is connected to the loading cam device using the pinion carrier as an output means for the cam disc of the loading cam device. Thus, for rotatably supporting the planetary gear unit, the connection between the pinion carrier and the cam disc has to be made by a separate member which straddles the annular wall member. Thus, in this transmission, the number of parts used is increased, which causes difficulty of assembly and increase of cost.